Low-back facet joints !

The lumbar facet joints are pairs of small joints at the back of the lower spine; they block twisting and share the load with the disc.

Official name: Zygapophysial (facet) joints

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What it is

Pairs of small sliding joints at the back of the spine, one on each side between neighbouring vertebrae, each with cartilage and a capsule.

What it does

Guide and limit movement (lumbar facets block twisting), and share the load with the disc, especially when you lean back.

Key facts

Where: Between articular processes from L1–L2 to L5–S1 (zygapophysial joints)
Function: Synovial joints; curved near-sagittal facets allow flexion-extension and block rotation; more coronal at L5–S1, resisting forward slip; nerve: medial branches of two dorsal rami

Relations

In front: Ligamentum flavum blending with the front of the capsule; just in front, the lateral recess with the traversing root and the foramen with the exiting root
Behind: Multifidus, which grips the capsule and the mamillary processes; further out, the erector spinae
Medial: Lamina and spinous process; inside the canal, the dural sac with the cauda equina
Lateral: Root of the transverse process, where the medial branch runs in a groove under the mamillo-accessory ligament

How to find it

The joints lie deep to the erector spinae, a few centimetres from the midline, at about the level of the gap between two spinous processes. In the paraspinal (Wiltse) approach the facet is the first bony landmark felt between multifidus and longissimus.

Examination

Facet loading (Kemp) test: standing, the trunk is extended and rotated toward one side; local back pain on that side suggests a facet source, and leg pain below the knee suggests a nerve root. It is not reliable on its own; controlled medial branch blocks are the reference

On imaging

CT shows facet arthropathy best: joint narrowing, osteophytes, subchondral cysts and a vacuum phenomenon. MRI shows effusions and synovial cysts; a large effusion with a slip suggests instability. On the oblique radiograph, a 'collar' on the neck of the Scottie dog marks a pars defect.

Common problems

Facet arthritis: low back pain that is often worse leaning back or twisting, and stiff in the morning.
Facet cysts that can press on a nerve root.
Worn facets allow one vertebra to slip on another (degenerative spondylolisthesis).

How it is diagnosed

There is no single sign. CT or MRI show arthritis; a numbing injection of the nerves to the joint (medial branch block) shows whether the joint is the pain source.

Treatment

Physical therapy, medicine, facet joint or medial branch injections.
Radiofrequency ablation: heat turns off the small nerves to the joint for months.
In a TLIF the facet on one side is removed to reach the disc.

Clinical notes

Spondylolysis in adolescents who repeat extension and rotation (gymnastics, cricket fast bowling, football); bilateral defects can lead to isthmic spondylolisthesis, usually L5 on S1
Facet hypertrophy plus ligamentum flavum thickening give the trefoil canal and lateral recess stenosis
The medial branch groove at the root of the transverse process is the fluoroscopic target for medial branch blocks and radiofrequency neurotomy in facet syndrome

Anatomical variants

Facet tropism: the left and right facets face different angles, most often at the lower lumbar levels; its link with disc herniation is debated

Memory aid

Scottie dog on the oblique view: eye = pedicle, ear = superior articular process, nose = transverse process, neck = pars, front leg = inferior articular process.

Test yourself

Think of the answer, then tap the question to see it.

Which nerves supply the L4–L5 facet joint?

The L3 and L4 medial branches of the dorsal rami: each lumbar facet joint receives two medial branches, so a block must target two nerves.

Which movement do the lumbar facet joints block, and why?

Rotation: their curved, near-sagittal facets allow flexion-extension but block twisting; at L5–S1 they are more coronal and resist forward slip.

What does a collar on the neck of the Scottie dog on an oblique lumbar radiograph mean?

A pars interarticularis defect (spondylolysis): the neck of the dog is the pars, the stress-fracture site between the upper and lower facets, most often at L5.

Why is degenerative spondylolisthesis most common at L4–L5?

The facets at L4–L5 face sagittally, which favours forward slip once the facets wear.

What is the reference test to confirm that a lumbar facet joint is the pain source?

Controlled medial branch blocks; the facet loading (Kemp) test suggests it but is not reliable on its own.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): articulationes zygapophysiales TA2 1707
Official Spanish (DeCS): Articulación cigapofisaria DeCS D021801
English (TA2): Zygapophysial (facet) joints
Also called: facet joints · juncturae zygapophyseales · zygapophysial joints

Sources: Terminologia Anatomica (TA2); DeCS; Anatomy, Back, Lumbar Spine.

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Representative model, for educational purposes only.

Low-back facet joints highlighted on the Durgical 3D model